1. Field of the Invention
The present invention relates to a magnetic head slider assembly comprising at least one transducer for reading and/or recording information contained on a data carrier. It is more particularly applicable to magnetic reading and/or recording transducers utilized in magnetic peripherals of data processing systems, in particular disc memories.
2. Description of the Prior Art
The use of magnetic disc memories in data processing systems is becoming more popular due to their storage capacity and the relatively short time taken by the reading and/or recording transducers (also called read and/or write transducers) to access data contained anywhere on the discs from the moment when the transducers receive an order to access this data.
Generally, magnetic discs carry data on concentric, circular recording tracks whose radial width does not exceed a few hundredths of a millimeter and which cover the major proportion of both faces of the discs. The discs, which are parallel, coaxial, and generally of the same diameter, are driven at a constant speed of rotation by an electric motor. Current practice is to associate a single transducer with each face of the disc. If it is desired to substantially reduce the time taken to access all the information contained on the disc face, several transducers, not exceeding 10 or 20 units in number and less than the number of tracks, are associated with the disc face. In the remainder of the text, the expression "disc face" will imply the association of the latter with one or more transducers.
Generally, transducers associated with one disc face are carried by the same main body of the transducer assembly and are mounted on a platform. This latter platform further comprises a suspension device fixed to the main body and to a movable rigid arm.
Platforms fall in two general categories, either a movable type platform or a fixed type platform. Movable type platforms are displaced radially above the face of the disc face with which they are associated to permit the transducer to access all the information contained in the latter. In this case a movable arm is mounted on a carriage which is displaced externally of the disc. Fixed type platforms, on the other hand, remain permanently stationary above clearly defined tracks on the face of the disc with which they are associated during the reading and/or recording operations, and each of the transducers contained within the platform remains associated with one and the same track. The platforms used most frequently in current practice are moving type platforms.
Usually the transducers are formed by a magnetic circuit around which is placed a winding and which has an air gap. This winding is connected by input and/or output electric conductors to the electronic circuits for reading and/or recording on a disc memory. The variation of induction within the air gap of each transducer permits the reading and/or recording of data contained on the face of the disc.
Generally, but not exclusively, the main body of the platform is in the shape of a relatively shallow right-angles parallelepiped of which a first "major face", which is opposite the face of the disc, contains the air gap or air gaps of the transducer(s), the second "major face" containing the input and/or output lead conductors of this (these) transducer(s). In the course of rotation of the disc, a cushion of compressed air is formed between the disc and the first "major face" often main body, which prevents the body from touching the disc and thus from damaging it. It is therefore said that the main body flies above the disc. The distance between the airgap (airgaps) of the transducer(s) and the disc face is called "flight altitude" or indeed "flight height" of the main body. It is usually of the order of some tenths of microns. The air cushion exerts pressure on all or part of the first "major face" of the main body normal to the latter and directed towards its second "major face". The part of the first major face which is under pressure of the air cushion is termed the "flight surface". The force resulting from this is termed lift force of the main body. It is a function of the flight surface. Dynamic equalibrium of the main body in flight is obtained by opposing the lift force with a force equal and opposite to it, called the "loading force" which is generally applied to the second "major face".
When the disc is not turning, the main body occupies a so called "rest" position with regard to it. In current practice there are used more and more frequently main bodies of platforms whose flight surface, in its rest position, is in contact at least partially with the disc face. Such main bodies are called "main bodies with unstick" contact. Generally available platforms comprising such main bodies are manufactured, for example, by the "Applied Magnetic Corporation" under the reference Winchester 3304 and 3306, and are known as the "Winchester" platform.
The main body of such a platform is constructed in the following manner: One or more gulleys (also called grooves), the depth of which is greater than or equal to 30 microns and may be as much as a few tenths of a millimeter, are formed in its first "major face". As a result there are several projecting portions, termed skids, on this major face.
An aeronautical analogy may be given using the terminology used in aeronautics. The main body may be likened to the wing of an aircraft. Air runs along the wing body in the direction of movement of the disc reaching, first of all, a face of the main body known as the "leading edge" which is perpendicular to the first "major face" and to the direction of movement of the disc. The other face of the main body, which is parallel to the leading edge, is termed the "tail edge".
The flight surface comprises two parts, namely: A first part, known as the main flight surface, which rests on the disc when the main body is in the rest position. It connects the tail edge to the main body. A second part, known as a separation surface, in the form of a bevel, is inclined to the main flight surface and extends it by connection with the leading edge. To move the main body from its rest position to its flight position above the disc, it is only necessary to rotate the disc sufficiently to develop a lift force. In quite a short time the body will unstick or separate from the disc due to the lift force. When the disc reaches its nominal speed of rotation the body will fly above it, its main flight surface being inclined towards the disc. The angle of inclination is in the order of a few milli-radians, the lift force being enough for body flight to be stable.
The drawback of conventional "main bodies with unstick contact" is that they rub against the disc during the unstick period which, as seen above, is relatively long. This results in wear both on the disc and the flight surface.
Before proceeding with a discussion of the invention, the reader may familiarize himself with the following U.S. Pat. Nos. and applications for patent for a better understanding of the prior art and problems associated with slider assemblies for magnetic transducers: 3,657,710; 3,678,482; 3,855,625; 4,081,846 and Ser. Nos. 958,840 (Plotto) filed Nov. 8, 1978, now U.S. Pat. No. 4,212,044; 034,747 (Lazzari) filed Apr. 30, 1979, now U.S. Pat. No. 4,258,400; and 737,725 (Desseri) filed May 10, 1978, now U.S. Pat. No. 4,261,024. The latter pending applications for patent are all assigned to the assignee of the present invention.
With the terminology adopted, the flight altitude is never nil even if the lubricating layer of the main body and the lubricating film of the disc are in contact. In this condition, the flight of the main body is said to be hydrodynamic and not aerodynamic. The definition of the flight surface as specified above for aerodynamic flight can be extended to any type of hydrodynamic flight. The flight surface is thus that part of the face of the main body on which the lift force, whether it is aerodynamic or hydrodynamic, is exerted.
It is known from current practice that magnetic discs may be covered with a lubricating film for protection of the magnetic recording layer.
The properties of monomolecular lubricating layers as well as the different methods for depositing them on solid surfaces are well known. They are described, for example, in the thesis of M. TADEUSZ G. MATHIA given in Lyon on Oct. 16, 1978 under the title "Study of Sliding Interface of Monomolecular Lubrication". Reference may also be made to GAINES: "Insoluble Monolayers At Liquid-gas Interfaces" published by John Wiley, New York (1966) and TABOR D. "Friction, Lubrication, Wear" in Surface and Colloid Science volume 5, edited by E. MATIJEVIC, John Wiley (1965).
Lubricating monomolecular layers comprise long chain and polar termination organic molecules. The probability of these terminations having an unequal electric moment is very great. These are, for example, organic molecules of fatty acid which have the property that they can be absorbed by the metal surfaces on which it is desired to deposit them with a high bonding energy, by means of their polar terminations. The free ends of these molecules form a sort of fibre mat, as described in the aforenoted thesis of Mathia, formed by an arrangement of "Methyl CH.sub.3 " groups of very low superficial energy. This explains the lubricating properties of these monomolecular layers (also called Monolayers or limited lubrication layers.)